The present invention relates to a method and an apparatus for repairing defects in emulsion masks and the like, and, in particular, to an apparatus and a method for removing defective portions existing in emulsion masks which are a type of photomasks used in the lithographic processes that is one of the processes for the manufacture of photoelectroformed products and photoetched products used for manufacturing semiconductors and the like, and for removing defective portions existing in patterns of organic layers (hereinafter also called emulsion masks) of color filters for LCD and CCD.
In recent years, increasingly fine patterns are required in connection with higher levels of integration of IC and LSI, and the patterns of semiconductor elements have tended to have higher levels of accuracy and quality. Apart from semiconductor elements, high accuracy and high quality are also required in the case of, for example, photoetched products such as shadow masks for color televisions, print circuit boards, electrodes for various types of display tubes and the lines of optical measuring apparatus, and in the case of photoelectroformed products such as meshes for camera tubes, electron microscope meshes, and other meshes for filtering. The recent photofabrication technology has enabled the achievement of degrees of fineness and accuracy that were not possible with the conventional mechanical process method, and a high accuracy of pattern is required for the photomasks used in the photofabrication technology.
In such photomasks that require a high pattern accuracy, it is necessary to repair small defects that occur in the mask manufacturing process.
Currently, photomasks are classified by their materials, into two types of emulsion masks and hard masks. Emulsion masks have a high-resolution photographic emulsion applied to the surface of a glass substrate.
Ordinary emulsion layer of the emulsion masks can be of either a silver emulsion or a non-silver emulsion, and the thickness of the layer is usually from 2 to 6 .mu.m. Hard masks have a light intercepting metal film such as that of chrome, ferric oxide or tantalum, for example, deposited onto the surface of a glass substrate using either the vapor deposition or spattering method to form a film with a thickness of approximately 0.1 .mu.m.
The defects that can occur in the photomask manufacturing method are black defects such as black dots and the like, and white defects such as pinholes and loss, etc. The method of correcting black dots and pinholes differ according to the type of photomask.
In the case of hard masks, the specific method that is generally used to repair black dot defects such as a black spot or a protruding portion is to apply to the area other than the defects a photoresist or mask of a material that does not corrode the metal layer and to then remove the defects by etching. In the case where fine black dot defects of the order of 1 .mu.m have to be removed, then a positive resist such as the OFPR resist (product of Tokyo Oka Kabushiki Kaisha) is applied and then the light from a mercury lamp is focussed with a size of approximately 1 .mu.m onto the resist on the defect to expose the resist. The exposed resist is then removed by developing processing and then an etching liquid is used to remove the light intercept metal film.
In the case of emulsion masks, the method of repairing defects is different because the emulsion layer is thick and there is no corrosive liquid such as used in the case of metals. For example, one of the methods for repairing black dot defects is to cut out the defect using the sharp end portion of a cutter knife or the like but the application of this method is limited to those instances where accuracy is not required or where those portions having defects are not connected to or adjacent to those portions that do not have defects. This method is not suitable for repairing the photomasks used for semiconductor manufacture or for fine processing. A repairing method using a YAG laser has been proposed in order to eliminate this deficiency. (Japanese Patent Laid Open Publication No. 60-207335)
In the case of a hard mask, white defects such as a pinhole or missing portion are removed by a method that involves applying a photoresist to the entire surface of the mask, exposing the portion of the photoresist on the fault and then developing the photoresist so that only that portion of the resist that was on the defect is removed. Thereafter, in this status, by using either the vapor deposition or the spattering method, a light intercepting film of a metal such as chrome is formed. Then, separating the photoresist leaves the light intercepting film only on the defects so that white defects such as pinholes and the like are rendered light-intercepting.
Hard masks have dimensions in the order of several inches square but the size of emulsion masks is large and is in the order of 20 to 40 inches. For this reason, in the case of the emulsion masks, the series of methods described above, which use vapor deposition and spattering, require large-scale coating apparatus and large-scale vacuum apparatus and the like. Since this is difficult as far as the facilities are concerned, it is more general to cover the defect by India ink applied manually using a brush having a fine hair tip.
With the pattern repairing method described above for black dot defects, a YAG laser with a wavelength of 1060 nm and a second harmonic of 530 nm enables fine defect repair, but the portion around that portion for which removal processing was performed swells. In addition, the removal of the defect portion cannot be made linear and so there is the problem of ruggedness.
When a YAG laser is used for defect removal, the swell of the peripheral portion of the defect amounts to 50% of the thickness of the layer and this becomes a cause of improper contact in uses where contact exposure is performed, thereby causing problems for its practical use. In addition, the non-linearity of the removed portion also presents a problem of quality now that finer patterns are being required.
In addition, the previously described method for the repair of white defect has its application limited to those which do not require precision and for which the defects are not connected to or adjacent to portions that do not have defects, and it is not possible to use it for the repair in the case of photomasks used for semiconductor manufacturing or fine processing.